Control method for feeding items on a conveyor

ABSTRACT

The feed of items from the discharge end of a fixed conveyor on to a second conveyor which is mounted for longitudinal movement relative to the first conveyor to achieve an equal spacing of the items on the second conveyor irrespective of the relative positions of the first and second conveyors is controlled by sensing an item conveyed by the second conveyor shortly after deposition thereon from the first conveyor and preventing discharge of an additional item on to the second conveyor until the first item has been sensed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 454,792 filedMar. 26, 1974 (now U.S. Pat. No. 3,928,114) which relates to anapparatus for use in building of structural components from buildingblocks such as disclosed in U.S. Pat. No. 3,855,752.

FIELD OF INVENTION

This invention relates to a control method for a conveying system.

BACKGROUND TO THE INVENTION

In the construction of buildings, generally a plurality of individualbuilding blocks is juxtaposed and joined to one another at the buildingsite to provide the requisite structure, for example, a wall.

Prefabricated structural panels have been suggested. However, suchprefabricated panels generally either lack structural strength inflexure or buckling resistance or are bulky and unwieldy. The panels ofthe aforementioned application, however, suffer from neither of thesedefects and consist of a plurality of courses joined in superimposedmanner throughout the height of the panel. Each of the courses consistsof a plurality of structural rectangular parallelepiped masonry blocksjoined in abutting longitudinal relationship. The blocks in thevertically adjacent courses are offset from one another.

The panels are formed from a family of blocks as described in theaforementioned U.S. Pat. No. 3,855,752, allowing the provision of aplurality of different types of joint with other panels. The majority ofblocks in the panel have a central core extending from the top face tothe bottom face of the block and a recess in each end face. The opposedrecesses in the end face of each two abutting blocks define a void ofsubstantially the same cross-sectional dimension as the central core,the voids coinciding with the central cores of the vertically adjacentblocks in the panel.

A plurality of satellite cores, each extending from the top to thebottom face of the block, is provided in each block, one pair beingpositioned between the central core and one of the recesses and theother pair being positioned between the central core and the other ofthe recesses. One member of each pair of satellite cores is closer toone longitudinal edge of the block than the other member. The satellitecores in blocks in vertically adjacent courses coincide with one anotherand define continuous passages throughout the height of the panel whichare out of fluid flow communication with the continuous passages definedby the coinciding voids and central cores. The satellite core-definedpassages are capable of receiving reinforcement rods therein forreinforcement of the panel, if desired.

The end blocks of each course are compatible with the other blocks inthe course and are appropriately chosen from the set of blocks, whichincludes, in addition to the blocks described above, a block in which arecess is formed in only one of the end walls and a block of half thelength of the others also having a recess only at one end, omitting thecentral core and having just two satellite cores.

The panels constructed in accordance with this prior invention, whileextremely useful in providing satisfactory structural members requirelabor-intensive and/or time-consuming procedures of production. Theblocks require indexing to ensure correct end block form and lateraldimension of the panel, appropriate application of adhesive and buildingup of the panel to the required height from the blocks to which theadhesive has been applied. In the parent application out of which thisapplication is divided, there is disclosed machinery allowingmechanization of the procedures involved in the production of structuralpanels in accordance with the abovementioned U.S. Pat. No. 3,855,752 andcomprising a first longitudinally extending conveyor having asubstantially fixed position and a second logitudinally extendingconveyor mounted on a track for driven reciprocal longitudinal movementso that a variable portion of the second conveyor is located below thefirst conveyor at any time.

SUMMARY OF INVENTION

The present invention provides a control method for controlling the feedof items from the discharge end of the first conveyor to the secondconveyor to space items apart on the second conveyor a substantiallyfixed distance irrespective of the proportion of the second conveyorlocated below the first conveyor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic elevational view of an apparatus of FIG. 2 forbuilding a panel structure and incorporating the control system of thepresent invention.

FIG. 2 is a perspective view of an adhesive-applying apparatus for usein the apparatus of FIG. 1;

FIG. 3 is a perspective view of part of the feed rollers, with partsremoved, immediately upstream of the adhesive-applying apparatus;

FIG. 4 is an elevational view of the adhesive-applying apparatus of FIG.2;

FIG. 5 is a perspective view of a masonry block having adhesive appliedthereto;

FIG. 6 is a sectional view taken on line 6--6 of FIG. 1;

FIG. 7 is a perspective view of a panel building platform for use in theapparatus of FIG. 1;

FIG. 8 is a front elevational view of the building platform of FIG. 7;

FIG. 9 is a part-sectional side elevational view of the buildingplatform of FIG. 7; and

FIG. 10 is a schematic diagram of the pneumatic circuit for operation ofthe adhesive-applying apparatus of FIGS. 2 to 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIGS. 1 and 6, an apparatus for use in theconstruction of building panels includes a first conveyor 10 forconveying concrete blocks along its length and having a substantiallyfixed elevated position supported on legs 11, and a second conveyor 12for conveying concrete blocks along its length, the second conveyor 12being mounted in any suitable manner on parallel tracks 14 forlongitudinal movement along the track 14 upon actuation of motor 16. Thesecond conveyor 12 is located, at least in their adjacent areas, belowthe level of the conveyor 10. A chain 17 is associated with secondconveyor 12 and is located in driving relation with the motor 16.

The movable conveyor 12 includes a substantially horizontal firstportion 18 mounted by wheels 20 on tracks 14 and a second portion 21pivotally mounted relative to the first portion 18 for pivotal movementbetween a substantially horizontal position to inclined positions. Thesecond portion 21 of the movable conveyor 12 also is pivotally mountedto a platform assembly 22 mounted by wheels 24 on the track 14 so thatthe platform assembly 22 and the second conveyor 12 are articulated.

An adhesive-applying apparatus 26 for the application of adhesive toconcrete blocks is mounted relative to the stationary conveyor 10. Thestationary conveyor 10 includes a first portion 28 and a second inclinedportion 30 downstream of the adhesive-applying apparatus 26 and inclineddownwardly from the downstream termination of the first portion 28 ofthe stationary conveyor 10 to the horizontal portion 18 of the movableconveyor 12.

The conveying surfaces of the conveyors 10 and 12 may be provided in anyconvenient manner. For example, the conveyor 12 may have a drivenendless belt or one such belt for each conveyor portion 18 and 21drivably to convey the concrete blocks from their point of dischargefrom the stationary conveyor 10 to the platform assembly 22.

The conveying surface of the conveyor 10 may be in the form of parallelspaced transverse roller elements mounted in free-rolling manner, withthe exception of the length thereof immediately upstream of theadhesive-applying station 26 where such rollers are driven, as willbecome more apparent below in the description of FIGS. 2 to 5. Feed ofconcrete blocks to the adhesive-applying station 26 may be achieved inthis embodiment by gravity through a slight upward incline, from left toright, of the surface of the first portion 28 of the conveyor 10 to thedriven rollers immediately upstream of the adhesive-applying station 26.If desired, the conveying surface of at least the first portion 28 ofthe conveyor 10 may be provided as a driven belt or driven rollers.

Usually the conveying surface of the second portion 30 of the conveyor10 consists of a plurality of parallely-arranged free-rollingly mountedrollers. However, any other suitable form of conveying surface may beused.

Turning now to consideration of FIGS. 2 to 5, there is illustrated theadhesive-applying station 26, its operation, the second portion 30 ofthe stationary conveyor 10 and the construction of the conveyor 10immediately upstream of the adhesive-applying station 26.

The buttering station 26 includes an upright frame member 32 mounted infixed position on the ground in any convenient manner and a transverseframe member 34 extending substantially perpendicularly to the uprightframe member 32 vertically upwardly spaced from and transverse to theconveyor 10.

The upright frame member 32 supports a first pair of adhesive-applyingguns 36 for vertical reciprocation relative to the frame member 32. Thepair of guns 36 is mounted in spaced-apart relation on a plate 38 havingwheels 40 for movement on track 42 situated in the frame member 32.

The reciprocal movement of the pair of guns 36 is actuated by apneumatically operated piston 44. The piston 44 may be operated in anyother convenient manner, for example, hydraulically. The upper and lowerextremities of the reciprocal movement of the pair of guns 36 arecontrolled by limit switches 46 and 48 respectively, which are engagedfor actuation by a flange 50 on the plate 38.

The transverse frame member 34 supports a second pair ofadhesive-applying guns 52 for horizontal reciprocation relative to theframe member 34. The second pair of guns 52 is mounted in spaced-apartrelation on a plate 54 having wheels 56 for movement on track 58situated in the transverse frame member 34.

The reciprocal movement of the second pair of guns 52 is actuated by apneumatically-operated piston 60. The transverse extremities of thereciprocal movement of the second pair of guns 52 are controlled bylimit switches 62, 64 and 66 which are engaged for actuation by a flange68 on the plate 54. The limit switch 64 usually is inactive and thelimit switch 66 defines the lateral extremity of movement of the guns52. However, where a half length block is to have adhesive appliedthereto, then the limit switch 64 defines the lateral extremity ofmovement of the guns 52.

The limit switches 46, 48, 62, 64 and 66 control the motion andoperation of the pairs of guns 36 and 52 so that adhesive is appliedthereby to a concrete block 70 only on the side and top thereof adjacentthe edges. The adhesive utilized in this operation is any convenientadhesive which will not cure until the block 70 has been laid with otherblocks to provide the structural panel but, at the same time, issufficiently viscous to adhere to the surfaces of the blocks 70 to whichit is applied, usually in substantially bead-like form.

The adhesive is fed to the pairs of guns 36 and 52 in any convenientmanner and may be discharged therefrom pneumatically upon actuation of asuitable pneumatic device.

As may be seen more clearly in FIGS. 3 and 4, a reciprocating piston 72,actuatable in any convenient manner, typically pneumatically, isattached to a pusher plate 74 which is reciprocated transversely of theconveyor 10 to abut a concrete block 70 which is intended to haveadhesive applied thereto. The pusher plate 74 is intended to position ablock 70 in its correct position against a suitable stop member forapplication of adhesive by the pairs of guns 36 and 52. In addition, thepusher plate 74 acts to prevent actuation of the adhesive application inthe absence of a block 70.

A rod 76 is fixedly attached to the plate 74, extends longitudinally ofthe piston 72 and is supported by a bracket 78. A flange 80 is attachedto the rod 76 for engagement with limit switches 82 and 84. Normally,upon actuation of the plate 74 the limit switch 82 only is opened,whereas in the presence of a block of half the normal length, the limitswitch 84 is actuated, causing actuation of limit switch 64 therebycausing application of adhesive only over the desired lateral widthcorresponding to the block length.

A pressure switch is provided to be actuated when the block is properlyclamped between the pusher plate 74 and the stop member, allowingoperation of the adhesive-applying procedure.

The portion of the conveyor 10 at and immediately upstream of theadhesive-applying station 26 consists of rollers 86 and 87 which aremounted for rotation in frame arms 88. The rollers 87, situated directlybelow the transverse frame member 34 and on which the block 70 sitsduring the application of adhesive, typically four in number, are drivenby a motor (not shown) and drive belt 90. The rollers 86 upstream ofrollers 87 are separately driven by a motor (not shown) and drive belt92. The sets of rollers 86 and 87 usually are driven at differingspeeds.

A gate member 94 in the form of a plate is situated at the exit of theadhesive-applying station 26. The plate 94 is attached to a frame 96which is pivotally mounted by roller 98 to the frame arms 88 for pivotalmovement below the rollers 86 and 87 for reciprocation of the plate 94between a first position wherein a portion thereof projects above theplane of the top surface of the rollers 87 and thereby prevents movementof a block 70 downstream of the adhesive-applying station 26 and asecond retracted position wherein the plate 94 is wholly below the planeof the top surface of the rollers 87 and thereby allows a block 70 tomove downstream of the adhesive-applying station 26.

The movement of the frame 96 between the two positions is controlled bya pneumatically operated piston 100 through crank arms 102,transversely-mounted rod 104 and rollers 106 engaging the arms of theframe 96 and mounted on flanges 108 on the rod 104. Limit switches 110and 112 engageable by parts of the frame 96 are actuable at the upperand extremities, respectively, of movement of the plate 94.

A first photoelectric cell 114 is mounted on the frame 88 with a line ofsight immediately upstream of the plate member 94 to sense thepositioning of the block 70 in the adhesive-applying station 26. While aphotoelectric cell 114 is illustrated, any other desired block-sensingmeans may be used.

The downwardly-sloping portion 30 of the conveyor 10 allows a block 70to which adhesive has been applied and after discharge from theadhesive-applying station 26 to be fed to the conveyor 12. An escapementplate 116 is positioned adjacent the downstream end of the conveyorportion 30 and is mounted on a rotatable roller 118. The roller 118 isrotatable under the action of pneumatically-controlled piston 120through crank flange 122 to move the plate 116 between adownwardly-depending position, shown in dotted outline in FIG. 2,wherein a block 70 positioned on the conveyor portion 30 is preventedfrom passing from the conveyor 10 to the conveyor 12, and a secondposition, shown in full outline in FIG. 2, wherein a block 70 positionedon the conveyor portion 30 may pass to the conveyor 12 without hindrancefrom the plate 116, the movement of the escapement plate 116 beingactuated by a block passing a downstream photocell and being closed bylimit switch 123.

A second photocell 124, or other convenient sensing means, is positionedrelative to the conveyor portion 30 for sensing the presence of a block70 on the conveyor portion 30 thereby signifying vacation of theadhesive-applying station 26 for the next block 70.

A schematic representation of the pneumatic piping used in theadhesive-applying station 26 is illustrated in FIG. 10. An air supplysource 124 under suitable pressure is fed through a master valve 126 anda flow control system 128 to a master line 130. From the master line 130extend branch lines 132, 134, 136, 138 and 140 serving respectivelypistons 72, 100, 120, 44 and 60 through limit switch actuateddouble-acting solenoid valves 142, 144, 146, 148 and 150 respectively.

Third and fourth photocells 152 and 154, or any other convenient blocksensing means, are positioned in longitudinally spaced-apart relationrelative to the conveyor portion 18 to sense the presence of movingblocks 70 on the conveyor portion 18 and to establish a predeterminedspacing between blocks on the conveyor 12. The function and operation ofthe photocells 152 and 154 are described in more detail.

Turning now to consideration of FIGS. 7 to 9, there is shown in detailthe construction of the platform assembly 22 and its juxtaposition andrelation to its environment. The platform assembly 22 is intended to bemovable longitudinally along the tracks 14 at an operator-controlledspeed relative to a stationary panelization frame or jig 156 on which aprefabricated panel 158 may be formed. A further panelization frame orjig 160 usually is positioned on the other lateral side of the platformassembly 22 from the building frame 156, on which a further panel may beprefabricated. More than one panel 158, typically up to three, may beformed on each jig 156, 160 if desired by superimposing one panel onanother.

The panelization frames 156 and 160 may be of any convenient form andgenerally the building face is inclined to the vertical away from theplatform assembly 22 as may be seen from FIG. 7. The panelization frames156 and 160 may be provided by self-standing A-frame structures.

The limits of longitudinal travel of the platform assembly 22 aredesigned to correspond to the length of the frames 156 and 160 andover-running safety limit switches 162 and 164 actuated by the wheels 24of the platform assembly 22 are provided.

The platform assembly 22 includes a base frame 166 to which is rotatablymounted the wheels 24 by which the platform assembly 22 moves on thetrack 14. An upright frame member 168 is rigidly mounted to the baseframe 166. Also rigidly mounted on the base frame 166 is a scissors liftstructure 170 of any convenient form which is hydraulically orpneumatically operated to raise and lower an upper frame member 172 byuse of piston 174. The limit of upward movement of the upper framemember 172 is dictated by limit switch 173.

The upper frame member 172 supports a substantially horizontal conveyorsection 176 for receiving the concrete blocks at the platform assembly22 from the conveyor portion 20 and drivably conveying the same on thetop surface thereof.

The conveyor section 176 is slidably mounted for vertical movement bywheels 178 on the upright frame members 168 for additional guiding ofthe upper frame member 172 during upward and downward movement thereofin response to the motion of the scissors structure 170.

A platform 180 is mounted on the upper frame member 172 for lateralmovement relative thereto. The platform 180 has rollers or wheels 182and 184 positioned in channels 186 and 188 respectively whereby thelateral movement of the platform 180 relative to the upper frame member172 may be achieved.

A rack and pinion gear system 190, controlled by a manual actuationwheel 192 and connecting shaft 194, is used to position the platform 180laterally with reference to the base frame 166, the platform beingcapable of movement to a position adjacent either panelization frame156, 160.

The lateral motion of the platform 180 allows the operator to compensatefor the greater distance from the platform of the frame members 156 and160 at increasing height and also to compensate the thickness ofsuccessive layers built up on the frames 156 and 160.

The platform 180 has a block conveying surface 196 consisting of aseries of parallely-arranged free-rolling rollers. The conveying surface196 is inclined downwardly from the driven conveyor 176 and receives theblocks 70 from the conveyor 176 for manual building of panels 158 by anoperator standing on the platform 180.

At the downstream end of the conveying surface 196 is located a limitswitch 198 actuatable by the pressure of a block on the rollers locatedat that point to cause the conveyor 12 to stop transporting blocks tothe platform assembly. The rollers concerned may be spring mounted inslots or in any convenient manner to achieve the desired switching. Oncea block is removed, the conveyor 12 operates again until a new block ispositioned on the switch 198. Normally the speed of delivery of theblocks to the platform assembly 22 is controlled to the building rate ofthe operator so that there is a substantially continuous movement of thebelt 12.

A plate-like surface 200 mounted on the platform 180 downstream of theroller conveying surface 196 to receive the forward portions of theblock 70 and to prevent overshooting of blocks from the conveyingsurface 196.

A foot-operated emergency brake switch 204 may be provided for asuitable use by operator. An operator-actuated control panel 202 ismounted on the platform 108 so that a variety of operations may becarried out by actuation of the appropriate circuitry.

For example, the control panel 202 may have controls including an on-offswitch for actuation of the entire system, a speed control to controlthe speed of the conveyor 10 and hence the speed at which blocks arereceived at the platform assembly 22, a speed control to control thespeed of longitudinal movement of the platform assembly 22, a scissorslift mechanism actuation control and a forward and reverse control.

An electrical circuitry control box 206 is mounted on the base member166 for reciprocal motion therewith. Electrical supply for the systemmay be provided in any convenient manner.

The panels 158, after sufficient time has elapsed for the adhesive toset, may be removed by an overhead crane or in any other convenientmanner, for grouting and/or reinforcement as desired.

OPERATION

In operation, concrete blocks 70, after grinding the upper and lowersurfaces thereof, if required, to provide smooth bedding planes, areplaced on the first portion 28 of the conveyor 10 by a first operator208 in indexed manner in the order the blocks are to be used in thestructural panel 158. The blocks 70 placed on the conveyor portion 28may be of any desired form, preferably as described in U.S. copendingapplication Ser. No. 295,896 referred to above, including blocks ofstandard length having recesses in both end faces, blocks of standardlength having a recess in only one end face, for use as an end-block andblocks of about half the standard length having a recess in only one endface, also for use as an end block.

The blocks 70 are gravity fed to the driven rollers 86 and 87 whichposition the lead block in the adhesive-applying station 26 against thegate plate 94 which projects above the plane on the surface of therollers 86. The first photocell 114 senses the presence of a block inthe adhesive-applying station and causes the drive of rollers 86 and 87to cease. The pusher plate 74 is actuated to situate the block in itsadhesive-applying position. Normally a standard length block hasadhesive applied to its upper and side peripheral edges, as illustratedin FIG. 5 by the guns 36 and 52. However, the adhesive-applyingmechanism may be controlled by a selector switch, not shown, to applyadhesive to the upper edges only, the side edges only or not at all,depending on the form and requirement of the block.

For example, a course end block will require no adhesive on its sideedges whereas a top course block will require no adhesive on its upperedges and a top course end block will require no adhesive at all.

Additionally, the limit switch 84 associated with the pusher plate 74 isintended to sense the presence of a half-length block and actuatecircuitry to cause limit switch 64 to constitute the transverseextremity of movement of the guns 52.

The adhesive-applying station 26 thereby applies adhesive automaticallyto the blocks in whatever manner is desired for the particular type ofblock and its intended position in the panel 158.

When the apparatus is in continuous operation when a block is situatedat the adhesive-applying station, another block, to which adhesive haspreviously been applied, is situated on the second portion 30 of theconveyor 10 against the escapement plate 116 and a further block,previously transferred thereto from the conveyor 10, is transported bythe moving conveyor belt 18 between the photocells 152 and 154.

When the block on the moving conveyor belt 18 is sensed by the photocell154 as it passes the same, the escapement plate 116 is opened allowingthe block retained thereby to pass from the second portion 30 of theconveyor 10 onto the moving conveyor belt 18.

When the latter block is sensed by the photocell 152, which signifiesthe presence of that block on the moving conveyor belt 18, theescapement plate 116 is reclosed.

At the same time, the gate plate 94 is retracted below the plane of thesurface of the rollers 86 and upon actuation of the limit switch 112 therollers 87 recommence rotation and eject the block to which adhesive hasbeen applied onto the second portion 30 of the conveyor 10, its presencethereon being sensed by the photocell 124 positioned one block-widthsdistance downstream of the photocell 114.

After the block to which adhesive has been applied has moved out of theadhesive-applying station 30 as sensed by the photocell 124, the gateplate 94 returns to its original position to stop the next block fed tothe adhesive-applying station 26, and the procedure is repeated.

The conveyed block, after being carried past the photocell 154, istransported by the moving surfaces of the conveyor portions 18 and 20 tothe platform assembly 22 and onto the rollers 196 and plate 200 thereof.

A block positioned on the skid plate 200 and engaging the rollersassociated with the limit switch 198 prevents further motion of theconveyor 12 until the block has been removed. An operator 210 removesthe block from the skid plate 200 and positions it appropriately on thepanel 158 he is constructing. Upon the removal of the block, theconveyor 12 recommences the forwarding of blocks to the platform 22.

As indicated above, however, usually the rate of delivery of the blocksto the skid plate 200 is controlled by controlling the speed ofoperation of the conveyor 12 to conform to the building rate of theoperator, so that the conveying surface of the conveyor 12 is insubstantially continuous motion and there is a substantially continuousflow of blocks to the platform assembly 22.

The operator 210 positions the platform 180 in an appropriate verticallocation by actuation of the scissors lift mechanism and an appropriatelateral location by actuation of the rack and pinion mechanism 190 byuse of the wheel 192.

The operator 210 builds up the desired panel 158 usually a course at atime. The drive motor 16 is actuated for each block removed from theplate 200 hence moving the platform assembly 22 on the track 14 relativeto the length of the panelization frames 156, 160. For a synchronousrate of removal of the blocks from plate 200, the motion of the platformassembly 22 is continuous. The longitudinal movement of the platformassembly 22 causes longitudinal movement of the conveyor 12 on the track14 from one side extremity of the panel 158 to the other during thebuilding of each course. As the platform assembly 22 moves towards theadhesive-applying station 26, the conveyor portion 18 is wheeled underthe conveyor 10 and, during movement of the platform assembly 22 awayfrom the adhesive-applying station 26, the conveyor portion 18 iswheeled out from under the conveyor 10.

This motion during the building of a course would normally result inblocks arriving at a slower or faster rate at the skid plate 200depending on the relative speeds and directions of travel of theplatform assembly 22 and the conveyor feeding the adhesive-applyingstation 26. In the present invention, the photocells 152 and 154 and theescapement plate 116 operate to maintain a substantially constant flowrate of blocks to the plate 200 at a predetermined spacing irrespectiveof the direction of travel of the platform assembly 22 and the relativespeeds of the conveyor 12 and the conveyor feeding the adhesive-applyingstation 26.

Since the opening of escapement 116 and hence the positioning of a blockon the moving conveyor 12 is achieved by actuation of the photocell 154when a block passes the same, and the closure thereof and the movementof a further block into the escapement is achieved by actuation of thephotocell 152, the rate of feed of blocks onto the moving conveyor 12 isvaried depending on the relative position of the block immediatelyupstream the photocell 154 and the photocell itself at any one time.

In this way, the blocks reach the builder 210 at a substantiallyconstant rate which he may adjust to suit his work speed by altering thespeed of the conveyor belt 12. In addition, he may adjust the speed oflongitudinal movement of the platform assembly 22 along the track 14.

SUMMARY

It will be seen, therefore, that the present invention provides acontrol system for use with panelization equipment utilized in theproduction of prefabricated structural panels.

Modifications are possible within the scope of the invention.

What I claim is:
 1. In a conveying system comprising a firstlongitudinally extending conveyor means having a conveying surface forconveying items longitudinally of said first conveyor means and adischarge end, said first conveyor means having a substantially fixedposition, said first conveyor means also having an openable gate meansat said discharge end for controlling the discharge of items from saidfirst conveyor means; a second longitudinally extending conveyor meanshaving a conveying surface for conveying items longitudinally of saidsecond conveyor means and a discharge end and being situated adjacentsaid first conveyor means to receive items from said discharge end ofsaid first conveyor means, said second conveyor means being mounted forreciprocal movement longitudinally thereof and longitudinally of saidfirst conveyor means to provide a variable portion of said secondconveyor means vertically below said first conveyor means; and first andsecond item sensing means located in longitudinally spaced relationadjacent said second conveyor means in fixed position relative to saidfirst conveyor means spaced from and downstream of said discharge end ofsaid first conveyor means with said first item sensing means beingspaced a distance from said discharge end of said first conveyor meanswhich is greater than said second item sensing means;a control methodfor controlling the feed of items from said discharge end of said firstconveyor means onto the conveying surface of said second conveyor meansduring longitudinal movement of said second conveyor means relative tosaid first conveyor means comprising feeding items from said dischargeend of said first conveyor means onto said conveying surface of saidsecond conveyor means by selective actuation of said gate means whilesaid latter conveying surface is in motion to convey said fed itemstowards the discharge end of said second conveyor means whereby aplurality of items are situated in longitudinally spaced-apart relationon said conveying surface of said second conveyor means, sensing a firstitem fed from said discharge end of said first conveyor means andlocated on said conveying surface of said second conveyor means by saidfirst sensing means, and opening said gate means in response to saidsensing to allow another of said items to pass from said discharge endof said first conveyor means onto said conveying surface of said secondconveyor means; said sensing said another of said items located on saidconveying surface of said second conveyor means by said second sensingmeans, and closing said gate means in response to said latter sensing,whereby said selective actuation of said gate means is achieved and saidfeed of items from said discharge end of said first conveyor means ontosaid conveying surface of said second conveyor means is controlled inresponse to said longitudinal movement of said second conveyor means tomaintain said items spaced apart substantially the same distance on saidconveying surface of said second conveyor means irrespective of therelative longitudinal positions of the discharge ends of said first andsecond conveyor means and the portion of said second conveyor meanslocated vertically below said first conveyor means.